Quartz to metal seal



g 6, 1952 E. H. NELSON 2,6o7,9s1

QUARTZ TO METAL SEAL Filed Aug. 6, 1948 ll I l XFN/Gan hev: Evan fierbert NeLson, g M?. 3

I H& A t borneg Patented Aug. 26, 1952 QUARTZ TO METAL SEAL Evan HerbertNelson, Middlesex, England, assignor to ,General Electric Company, acorporation of New York j Application August e, 1948, Serial No. 42,823In Great Britain August 8, 1947 1 Claim. (CI. 29-188) This inventionrelates to seal bodies of the type wherein a conductor is hermeticallysealed through a wall of vitreous material of low thermal'expansion'coeflicient. such as quartz. The invention also relates to electricdischarge devices, and especially high pressure gas-filled orvaporfilled discharge lamps 'having envelopes of low expansion vitreous.material incorporating such seal bodies.

In seal bodies of the type specified, it is often desirable that theconductor should-be a'stout A body ,v of tungsten, for example a stoutrod, but

thedifficulty arises that such bodies often cannot be sealed directly tothe vitreous material owin to the difference inthermal expansion whichwould result in cracking of the seal on heating. In one method that hasbeen proposed for overcoming this difculty, two collinear tungsten rodsare welded to, or abut under pressure against, opposite sides of a thinmolybdenum sheet whose edges are hermetically embedded in the vitreousmaterial. It has hitherto been difficult to unite the thin molybdenumsheet Satisfactorily with the tugnsten conductor for it is difli-` cultto weld the molybdenum to the tungsten. It has been proposed to usenickel sandwiched betweenthe molybdenum sheet and the tungsten forovercoming this difficulty in welding.

The principalobject of my invention is to provide improved seal bodesand improved methods for their fabrication. v

Further objects and advantages of the invention will appear from thefollowing detailed description of species thereof and from theaccompanying drawings in which Fig. 1 is an elevation, partly sectional,View of a seal body in the form of :a stem for an electricdischargequartz lamp; Fig. 2 is a fragmentary view of the metal parts of the sealbody assembled for being joined together; Fig. 3 is a similar View ofthe metal parts and the vitreous parts of the seal body assembled forjoining together to form the stern, and Fig. 4 is a similar view of themetal parts of a similar seal body.

Referring to Figs. 1 to 3 of the drawing, the lamp stem comprises astout tungsten conductor rod l which passes through an aperture in athin molybdenum sheet in the form of a disc 2 which is hermeticallyjoined to and around the tungsten conductor by the use of a solder orbrazing medium of metal, shown at 3, which unites both with molybdenumand with tungsten on heating. Part of the molybdenum disc 2 is embeddedin the vitreous material which i in the form of a tube 4 which supportsthe metal parts 2 of the stem. An electrode 5 of tungsten' is mounted onthe inner end of rod l. As shown, the edge 6 of the molybdenum disc istapered to form a sealing edge and is embedded in the tube 4 'ofvitreous material. The embedded part of disc 2 extends all the wayaround the rod I in order to complete the hermetic seal. One metal whichunites both'with molybdenum and tugnsten is nickel, but While this metalmay in some cases be used satisfactorily as a solder or brazing medium,I have found that it often attacks the thin molybdenum disc`2 so as toleave gapsbetween the disc and the tungsten conductor rod l.Accordingly, I prefer to use a molybdenum-rich' alloy of nickel andmolybdenum as the solder or brazing' medium. such an alloy may readilybe produced in situ in performing the soldering or brazing operation. i

Thus, in one method of forming theseal body,

described by way of example', the tungsten rod l i is passed through acentral ap'erture in the thin molybdenum disc 2, the' rod 'fitting thea'perture' closely as shown in Fig.' 2, A ring lof thin molybdenum wirefittingclosely around the tungsten rod is then placedaro'und the rod lin the corner between the rod l and the upper surface of the molybdenumdisc 2 and a 'similar ring 8 of nickel wire is placed next to the ringof molybdenum wire. h N V The rod l is held vertically with the wirerings 1 and 8 above the molybdenum disc 2, as shown,

and the rings are heated, for example in an 'elec- 'i tric oven in areducing atmosphere,`until the nickel ring 8 melts and flows down overthe molybdenum'ring 'I toform a molybdenumrich alloy which solders orbrazes the molybdenum,

disc2 to the tungsten rod l on cooling, as shown at 3 in Figs. 1 and 3.',To avoid oxidation, the heating is carried 'out in an electric oven ina reducing atmosphere such as forming gas, which is a mixture ofhydrogen and nitrogen; The seal,

body, after being formed, is allowed to cool in a similar atmosphereuntil below the oxidizing temperature of any of its parts.

The seal body is then joined to the vitreous part of the lamp stem inthe manner shown in Fig. 3 and similar to that described in BritishPatent 563,027, that is, the disc 2 is mounted between the flanges 9 andIO of two quartz tubes ll and l2 which extend beyond the'ends of the rodl. The outer edges of the flanges are then fused together without theedge 6 of disc 2 being embedded in them. In order to avoid oxidation ofthe disc during joining of the flanges, nitrogen is passed through theouter ends of tubes ll 3 and [2 until the edges of the flanges 9 and mare joined. The space enclosed by the joined tubes l l and IZ is thenevacuated and the fianges 9 and o are heated so that they collapse ontoand fuse with the disc 2, being, pressed thereon by atmosphericpressure. The parts of tubes l l and !2 near the dis"c 2 are thencollapsed onto the thin molybdenum foil sheets !3 andl4 wrapped aroundthe rod l before assembling the seal body in the tubes ll and !2 toprevent the uartz from fusing with rod l. then removed so as to eXposethe ends of the' end of rod I. The completed stem may be mounted on aquartz envelope by means of a 1-0 The excess tubing is rod l and theelectrode 5 is then .mou'nted on the quartz ring fused to the endportion of tube 4 nearest the electrode'. i (j The species of theinvention shown in Fig. 4

is similar to that shown in Figs. 1 to 3 except that the tungstenconductor rod does not pass through the molybdenum disc'2 but is in twoparts 15 and IE united to 'opposite 'sides of the disc 2 so that theyefiectively formprolongations of each other. In making such a seal body,the rods and the disc are ass'embled with' a'thin piece I? of amolybdenum rich alloy of nickel and molybdenum sandwiched betweenthe endof each rod and the face' of 'the disc'ag'ainst which it abuts. The sizeofpie'ces 'l'l has been exaggerated in the drawing& The assembly-is thenplaced for five 'minutes *in an'electric oven maintained at l500 andfilled with a' reducing atmosphere, such as forming gas; The brazedjointsbetween the 'disc 2 and theends of rods l5 a nd IB are then foundtobe formed oncooling 'of the assembly. The seal body 'may then bejoined to the vitreous' part of the stem' in the same-,manner describedin conjunction with Fgs. 1 'to-3.* V

Copper is a possiblealternative metal to nickel for use as the brazingmedium, though Copper should not be:used if:the-brazed joint is exposedto attack by mercury in use of the seal body as it would be if exposedon the inside of a high pressure mercury vapor discharge lamp. However,Copper may be used for the brazed joint between disc 2 and whichever rod`l5 or 16 extends to the outside ofthe lamp stern. i i

By 'brazingis meant, for the purposes of this invention, the joinng oftwo metals by heating them in juxtaposition with a third'metal, whichmay be analloy, of lower melting point, which unites with both and mayormay not melt during the heating. The terms-"so1der" and "brazing medium"are often use synonymously and both terms are used in this specicationin order to 'make it clear that no limitations are implied on thecomposition of suitable metals for joining the con'ductor and the discand that the metal may or may not melt during heating I Amolybdenum-rich alloy of nickel and molybdenum may, in many cases, beformed in stu during the brazing operation by heating molyb- Number NameDate 1,271,245= VonRec`k1nghausen; July 2', 1918 1 293',441-.Houskeeper' ;e Feb; 4,`I9I9" 1,733,744 Marden et al Oct'.^29 '19292,oo'5,256- Eitel im J'une-s, 193 5 1159305 Lenz et al i/1237 23; 19392,163,4o9 Pulfrich 'June :zd -1.939 2,2o7,38o Kurtz' ;J'i1y9; 19402,22o,96 Kern Nov,` 12,*1940 2,337,9o3 Hensel oet. 36,?1945-" 2 131363'Cherry Novi 25; 1'9'47 %64,591 Larsen Mar. 15, 1949-'` 57FOREIGN-PATENTSJ O Number Country y Date* r -563,027 Great Britain' n efiuly 26, 1944" formed preferably before the members of theseal'b'odyare assembled.

i Molybdnumrods may be used in place of rods 1 5; and lt. i

What `I claim as new and desire to secure by LettersPatent of the UnitedStates is:

The methodof hermetically uniting a thin molybdenum scaling disc for aquartz-to-metal seal body around a conductor rod of metal of the groupconsisting of tungsten and molybdenum which comprises the .stepspfproviding' the disc rod, placing the disc on the'ro'diwith 'the letterextending through the eperme; positio'niig molybdenum ring around the*rod and' immedi ately over the juncture between* the disc and m ing a:

atmosph'ere' 'until the metal of the s'eetmd'` ring i becomes molten andfiewsbv the' molybdenumring to form a molybde'r'ium rich alloywhich-fiowsnto and seals said j unctire;

' nVA nERB RTjNELsoN. REFERENCES: QTED f The' following references' areof'r'ecord. in'th file of this 'patent: p

UNITED 'sTATEs' ATEN s oTH-ER REFRENES" Aufbauder Zewiestofiiegierungenby Hansen;

(Copy in Pat; Off; scientific Lbrary 0 Publ. by Edward Bros.',-I`nc.,-Ann A-rbor; Mich;`

